1. Field of the invention
The present invention relates to an image forming apparatus such as a copying machine, etc. and more particularly relates to an image forming apparatus in which the adjustment of feeding start timing of a transfer sheet to the transfer section can be easily carried out.
2. Description of the prior art
In a conventional copying machine which can be an example of an image forming apparatus described above, as the optical system for exposing a document to a light and scanning the document starts scanning in an appointed scanning direction, a home position switch which is installed in the vicinity of the starting position of the optical system detects passage of the optical system. Consecutively, the timing switch which is installed at the downstream side in the scanning direction of the home position switch detects the passage of the optical system.
The fixing position of the home position switch is a certain index position at the scanning start of the optical system. The timing switch is used for synchronizing both the reading start of a document image by the optical system and the movement of the leading edge of the transfer sheet on which the document image is to be transferred. The distance between respective fixing positions of the home position switch and the timing switch is individually set on every copying machine according to the synchronization timing for synchronizing both tile reading start and the movement of leading edge of the transfer sheet.
And the copying machine is provided with a resist clutch which can intermittentably connect a resist roller to start the feeding of a transfer sheet to the transfer section with the drive source thereof. Therefore, the operation start timing of the resist clutch corresponds to the distance between the fixing positions of the respective switches.
Hence, in order to diminish dispersion of the response time of the resist clutch and dimensional dispersion of respective kinds of components, it is necessary to adjust the distance between tile fixing positions of the above switches. Then, for example, the timing switch can be installed so as to be able to move in the scanning direction, and the adjustment of the operation start timing of the resist clutch can be carried out by changing the fixing position of the timing switch.
Hence, a work for mechanically adjusting the fixing position of the timing switch to adjust the feeding start timing of the transfer sheet has been conducted, with trial and error repeated, by a skilled person having a pretty good skill as checking a document image transferred onto a transfer sheet. For this reason, the work has not been easy.
Even though the adjustment work can be done by, for example, a skilled person, it has not been possible that an adjustment work is carried out with a remarkably high accuracy and a small dispersion because the work is performed by a person.
Furthermore, it is general that such adjustment work has been set once on shipping the corresponding copying machine. Namely, the adjustment work is never performed by a user during the service life of the copying machine. Therefore, even though any gap in the synchronization timing should occur due to, for example, wearing of various kinds of components as time passes, the gap could not be corrected.